What is Interface?

Question:

What is Interface?

Answer:

Interface refers to matching between a sender and a receiver, with respect to connection. When a human being intends to transmit his or her thoughts verbally, for example, the words will not be able to be understood unless the person speaks loud enough and the other party intends to hear the words. Incidentally, "man-machine interface" means that a system supplies a display, voice, and/or operability that a human being can understand.
When two semiconductor devices are to be connected, the voltage and timing of the change of signaling of the two must be matched. For signaling, in addition to that of the TTL (Transistor-Transistor Logic) and CMOS levels (refer to Tea Breakunder Pull-up/pull-down ), the following high-speed interfaces using low-voltage signals or signal differentials are available.

Interface

Voltage

Termination

Standard

Speed example

Application example

LVTTL/LVCMOS

(Low Voltage TTL/
Low Voltage CMOS)

3.3V

JEDEC JESD8-B

350MHz

2.5V

JEDEC JESD8-5

350MHz

1.8V

JEDEC JESD8-7

250MHz

LVCMOS

1.5V

JEDEC JESD8-11

225MHz

HSTL Class I

(High-Speed Transceiver
Logic)

1.5V

JEDEC JESD8-6

150-225MHz

QDRSRAM

HSTL Class II

1.5V

JEDEC JESD8-6

150-250MHz

QDRSRAM

Differential HSTL

1.5V

JEDEC JESD8-6

150-225MHz

CLK interface

SSTL-3 Class I, II

(Stub Series Terminated
Logic)

3.3V

JEDEC JESD8-8

167MHz

SDRAM

SSTL-2 Class I, II

2.5V

JEDEC JESD8-9A

160-400MHz

DDR I SDRAM

Differential SSTL-2

2.5V

160-400MHz

DDR I SDRAM

GTL

(Gunning Transceiver
Logic)

2.5V 3.3V

JEDEC JESD8-3

200MHz

Backplane

GTL+

5V

JEDEC JESD8-3

133-200MHz

Backplane

LVDS

(Low Voltage Differential
Signaling)

3.3V

ANSI/TIA/ EIA-644

840Mbps

Signal transmission

LVPECL

(Low Voltage Positive
Emitter Coupled Logic)

3.3V 2.5V

ANSI/TIA/ EIA-612

840Mbps

SONET/SDH, Ethernet,1394

CTT

(Center-Tap-Terminated)

2.5V 3.3V

JEDEC JESD8-4

200MHz

Backplane-bus

PCI

(Peripheral Component
Interconnect bus)

3.3V

66MHz

PC

PCI-X 1.0

3.3V

133MHz

PC

AGP 1x, 2x

(Accelerated Graphics
Port)

3.3V

66-133MH

Image processing

When two systems are connected, matching of communication procedures (protocols) such as identification, sequencing, and checking is also necessary. Interfaces are divided into two types: serial and parallel. While a serial interface transfers data 1 bit at a time, making a waiting queue long, a parallel interface can transfer data of two or more bits at the same time. For example, a 133 MHz 64-bit parallel PCI has a bandwidth of up to 8.5 Gbps (133 M x 64). ISDN, which is a 128 kbps serial interface, is called a broad band system, but parallel interfaces can transfer an overwhelming quantity of data per unit time. Parallel interfaces, however, require two or more signal lines, and synchronizing these lines is a problem that must be solved.